Role of the steroidogenic acute regulatory protein (StAR) in steroidogenesis

Steroidogenic acute regulatory protein: its presence and function in brain neurosteroidogenesis

Neurosteroids are synthesized de novo and involved in a variety of physiological functions in the central and peripheral nervous systems. Although the steroidogenic acute regulatory protein (StAR) plays an essential role in the steroidogenesis of peripheral endocrine glands, its presence and role in the brain had been previously questioned because of difficulties in detecting it. However, a number of recent studies have confirmed the presence of StAR in rodent and human brains. Moreover, there is evidence suggesting that StAR plays a role in steroidogenesis in the brain, as it does in peripheral endocrine organs. The present review presents data regarding the presence and role of StAR in brain steroidogenesis, demonstrating the essential characteristics of the protein.

Effects of dehydroepiandrosterone on corticosterone release in rat zona fasciculata-reticularis cells

The decline of plasma dehydroepiandrosterone (DHEA) and maintenance of glucocorticoid levels with increasing age contribute to excess body fat accumulation, hyperglycaemia, hyperlipidaemia, hyperinsulinaemia and cancer. Although opposing actions of DHEA and corticosterone have been proposed in a rat model, the effects and action mechanisms of DHEA on rat adrenal zona fasciculata-reticularis (ZFR) cells are still unclear. This study addressed the effects of DHEA on corticosterone release, cellular cAMP production, the functions of steroidogenic enzymes and the expression levels of steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc). ZFR cells were incubated with DHEA in the presence or absence of adrenocorticotropin (ACTH), 8-Br-cAMP, forskolin, 25-OH-cholesterol, pregnenolone, progesterone or deoxycorticosterone at 37 degrees C for 30 min, 1 h or 5 h and the concentration of corticosterone or pregnenolone measured subsequently in the media by RIA. The cells were used to measure the content of cAMP by RIA and to extract protein for Western blot or mRNA for RT-PCR analysis. The data demonstrated that (1) DHEA inhibited ACTH-, 8-Br-cAMP-, 25-OH-cholesterol-, pregnenolone-, progesterone- or deoxycorticosterone-stimulated corticosterone release; (2) DHEA increased 25-OH-cholesterol-stimulated pregnenolone release but not when 25-OH-cholesterol was combined with trilostane; (3) DHEA increased the K(m) of 11beta-hydroxylase but not P450scc; (4) DHEA affected the expression levels of StAR protein but not of P450scc. These results suggest that DHEA acts directly on rat ZFR cells to diminish corticosterone secretion by inhibition within the post-cAMP pathway, by inhibiting steroidogenic enzymes downstream from P450scc and by inhibiting StAR expression.

Intratesticular delivery of tumor necrosis factor-alpha and ceramide directly abrogates steroidogenic acute regulatory protein expression and Leydig cell steroidogenesis in adult rats

Systemic or intratesticular release of TNF alpha and IL1 beta have been implicated in the reduced testosterone biosynthesis and impaired production of competent spermatozoa found in human patients suffering from sepsis or chronic inflammation. Although in vitro and in vivo studies have demonstrated that TNF alpha and IL1 beta intercept the hypothalamic-pituitary testis axis at different levels, the site(s) of action and relative contribution of each cytokine to the overall testicular failure associated to systemic inflammatory processes remains poorly defined. In this study we show that intratesticular delivery of TNF alpha induced a rapid (4 h) and sustained (up to 24 h) reduction in steroidogenic acute regulatory (StAR) protein expression and testosterone biosynthesis in nonstimulated or human chorionic gonadotropin-treated intact or hypophysectomized rats. Bilateral treatment with cell-permeant short-chain ceramides (C2-cer or C6-cer) reproduced the early (4 h) inhibitory action of TNFalpha on testosterone biosynthesis and testicular StAR expression. The inhibitory action of C2-cer or C6-cer was not observed in animals treated with inactive analogs (dihydroceramide), phosphorylcholine, sphingosine, or sphingosine-1P. In sharp contrast to the previously described ability of IL1 beta to prevent human chorionic gonadotropin-stimulated Leydig cell steroidogenesis in vitro, serum testosterone and testicular StAR protein expression remained unchanged in animals bilaterally injected with this cytokine. These data support the concept that TNF alpha triggers different effector mechanisms to directly inhibit Leydig cell StAR expression and steroidogenesis, which ultimately contribute to the global reproductive failure associated with chronic inflammation and sepsis.

Effects of 3,3',4,4',5-pentachlorobiphenyl, a coplanar polychlorinated biphenyl congener, on cultured neonatal mouse testis

3,3',4,4',5-Pentachlorobiphenyl (PCB126), a congener with a planar configuration, has been established to have relatively strong toxicities similar to those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via aryl hydrocarbon receptors. We investigated the effects of this coplanar PCB on mammalian early spermatogenesis and steroidogenesis in a mouse neonatal testicular organ culture system. Testes collected from newborn mice were subjected to organ culture in medium containing 0, 10, 100 or 1000 nM PCB126. Histochemical analysis revealed that the BrdU-labeling indices of both spermatogenic cells and Sertoli cells were unchanged in all testis specimens exposed to the coplanar PCB. CYP1A1 and steroidogenic enzymes (P450scc, P450c17, 3beta-HSD and 17beta-HSD) mRNA levels were determined by semiquantitative RT-PCR. The CYP1A1 mRNA level in cultured testis was significantly increased by PCB126 in a dose-dependent manner. Although mRNA levels of 3beta-HSD and 17beta-HSD were unchanged, the P450scc mRNA level was significantly down-regulated by PCB126 in a dose-dependent manner. In contrast, the P450c17 mRNA level was significantly higher in 1000 nM PCB126-exposed testis than in control testis. These results suggest that the coplanar PCB does not alter the proliferative activity of spermatogenic cells and Sertoli cells in neonatal testis, but that it directly affects the expression of steroidogenic enzyme genes.

Tissue growth and remodeling of the embryonic and adult adrenal gland

The adrenal gland provides a model system for the study of tissue remodeling in endocrine physiology. For example, proper adrenal development requires proliferation of the adrenogonadal primordia, separation of adrenal and gonadal precursors, and cell migration that unites the adrenal cortex and adrenal medulla. In the adult, normal adrenal function is assured by the adrenal gland's unique capacity for growth in response to both tissue injury and physiological demand. Identification of the molecular and genetic programs underlying tissue remodeling in the adrenal is important for understanding basic aspects of development and regeneration, as well as adrenal disease. Here, we will highlight the roles that nuclear receptors and pituitary hormones play in regulating fetal adrenal development and adult adrenal growth. In addition, we will review the most current data on how extracellular signaling pathways are coupled to the function of these important regulators of adrenal development and function.

Steroidogenic acute regulatory protein in ovarian follicles of gonadotropin-stimulated rats is regulated by a gonadotropin-releasing hormone agonist

The aim of the present study was to examine the acute and chronic effects of the gonadotropin-releasing hormone agonist (GnRH-a) leuprolide acetate (LA) on the expression of the steroidogenic acute regulatory protein (StAR), the cytochrome P450 side-chain cleavage enzyme (P450scc), and steroid production in antral ovarian follicles obtained from prepubertal equine choriogonadotropin (eCG)-treated rats. Follicular contents of StAR and P450scc proteins were measured by Western blotting following in vivo injection of eCG (control) and eCG+LA (LA) to prepubertal rats. Treatment with eCG for 2 h resulted in no change in StAR protein content, but it was markedly increased at 4 and 8 h after hormone treatment. However, coadministration of eCG+LA produced a significant increase (P < 0.05) in StAR protein levels at 2, 4, and 8 h when compared with eCG treatment. Acute and chronic treatment with either eCG or eCG+LA did not alter the P450scc protein levels in freshly isolated follicles. The increase in StAR protein expression following LA treatment was qualitatively similar to StAR mRNA expression, as determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. Furthermore, administration of eCG demonstrated a time-dependent increase (2-8 h) in the levels of StAR mRNA, and these levels were markedly increased by eCG+LA. However, the temporal response pattern of StAR mRNA was much greater at 2 h following LA administration when compared with controls. In addition, 48 h of LA treatment in eCG-treated rats resulted in a significant increase (P < 0.05) in follicular progesterone levels, whereas significant decreases in androgen (testosterone and androsterone) and estradiol levels were observed. Similar results were obtained when serum androgens and estradiol were measured, but serum progesterone levels were unchanged. Collectively, these findings demonstrate that the inhibitory effect of LA on ovarian androgen and estradiol levels is related to changes in the follicular levels of StAR protein and steroid production.

Immune-endocrine interactions and Leydig cell function: the role of cytokines

Inflammatory disease is known to affect male reproductive function and fertility. Male accessory gland infections (MAGI) account for almost 15% of all cases of male infertility seen in infertility clinics. Infections of the male accessory glands are associated with increased counts of white blood cells in semen and elevated levels of pro-inflammatory cytokines in the semen and the testis. Numerous studies have underscored the importance of cytokines in the regulation of testicular and glandular function during pathophysiological events as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this paper is to particularly review the role of cytokines in the regulation of Leydig cell function in the testis primarily under pathophysiological conditions, and also considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Inhibitory mechanisms of lead on steroidogenesis in MA-10 mouse Leydig tumor cells

Lead can directly influence Leydig cell steroidogenesis, which results in reduction of testosterone and causes low sperm counts in human beings and animals. This study investigated the effect of 6 h incubation time of lead on steroidogenesis in MA-10 mouse Leydig tumor cells. Lead acetate, ranging from 10(-8) to 10(-5) M, caused profounder inhibitory effects on human chorionic gonadotropin (hCG)- and dibutyryl cAMP (dbcAMP)-stimulated progesterone production for 6 h in MA-10 mouse Leydig tumor cells. Lead acetate significantly inhibited hCG- and dbcAMP-stimulated progesterone production from 20 to 35% in MA-10 cells at 6 h. Lead suppressed the expression of steroidogenesis acute regulatory (StAR) protein from 30 to 55%. Moreover, the activities P450 side-chain cleavage (P450scc) enzyme and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) were reduced by lead from 15 to 25%. Thus, after 6 h exposure to lead caused profounder inhibitory effects on StAR protein expression and steroidogenic enzymes and then progesterone production compared to 2- or 3-h lead treatments in MA-10 mouse Leydig tumor cells.

5'-p-Fluorosulfonylbenzoyl adenosine inhibits progesterone synthesis in human placental mitochondria

The human placental mitochondria have an ATP-diphosphohydrolase (apyrase) activity. In this paper we characterized the effect of 5'-p-fluorosulfonylbenzoyl adenosine (FSBA) on placental apyrase, and its repercussion on progesterone synthesis and oxygen consumption. Apyrase activity was inhibited by FSBA. Nucleosides tri- and diphosphates protected against FSBA inactivation, but divalent cations did not, indicating that FSBA attaches itself to an ATP-binding site of apyrase. In mitochondria, the inactivation of apyrase by FSBA was associated with inhibition of progesterone synthesis. Also, the oxygen consumption induced by ATP but not by ADP, was inhibited, clearly showing that FSBA exclusively inactivated the apyrase in human placental mitochondria. It is concluded that the apyrase activity is closely related to progesterone synthesis, probably associated with the cholesterol transport between mitochondrial membranes.

Scavenger receptor class BI and selective cholesteryl ester uptake: partners in the regulation of steroidogenesis

The steroidogenic tissues have a special requirement for cholesterol, which is used as a substrate for steroid hormone biosynthesis. In many species this cholesterol is obtained from plasma lipoproteins by a unique pathway in which circulating lipoproteins bind to the surface of the steroidogenic cells and contribute their cholesteryl esters to the cells by a 'selective' process in which the whole lipoprotein particle does not enter the cell. This review describes the lipoprotein selective cholesteryl ester uptake process and its specific partnership with the HDL receptor, scavenger receptor class BI (SR-BI). It describes the characteristics of the selective pathway, and the molecular properties, localization, regulation, anchoring sites and potential mechanisms of action of SR-BI in facilitating cholesteryl ester uptake by steroidogenic cells.

Inhibition of testosterone production by propylthiouracil in rat Leydig cells

Propylthiouracil (PTU) is a thioamide drug used clinically to inhibit thyroid hormone production. However, PTU is associated with some side effects in different organs. In the present study, the acute and direct effects of PTU on testosterone production in rat Leydig cells were investigated. Leydig cells were isolated from rat testes, and an investigation was performed on the effects of PTU on basal and evoked-testosterone release, the functions of steroidogenic enzymes, including protein expression of cytochrome P450 side-chain cleavage enzyme (P450(scc)) and mRNA expression of the steroidogenic acute regulatory protein (StAR). Rat Leydig cells were challenged with hCG, forskolin, and 8-bromo-cAMP to stimulate testosterone release. PTU inhibited both basal and evoked-testosterone release. To study the effects of PTU on steroidogenesis, steroidogenic precursor-stimulated testosterone release was examined. PTU inhibited pregnenolone production (i.e., it diminished the function of P450(scc) in Leydig cells). In addition to inhibiting hormone secretion, PTU also regulated steroidogenesis by diminishing mRNA expression of StAR. These results suggest that PTU acts directly on rat Leydig cells to diminish testosterone production by inhibiting P450(scc) function and StAR expression.

Marked inhibition of testosterone biosynthesis by the hepatotoxin nodularin due to apoptosis of Leydig cells

We previously observed that the serum testosterone level was greatly reduced in the course of diethylnitrosamine-nodularin-induced hepatocarcinogenesis in Fischer 344 male rats (Lim et al., Gastroenterological Carcinogenesis, 1999). As an extension of this observation, this study was undertaken to investigate the molecular mechanism of downregulation of testosterone and its effect on target organs in Fischer 344 male rats treated with the hepatotoxin nodularin. After treating the rats with nodularin, a marked reduction of the testosterone level was noted in both serum and testis, with an accompanying accumulation of cholesterol in serum. Reduction of serum testosterone was not due to increased degradation of testosterone in the liver but to impaired biosynthesis in the testes, reduced activities of the cholesterol side chain cleavage enzyme and 17alpha-hydroxylase, and decreased expression of the steroidogenic acute regulatory protein gene, all of which constitute rate-limiting steps for testosterone biosynthesis in the testes. Intraperitoneal injection of nodularin into rats induced cuboidal changes of glandular epithelium in ventral prostates and apoptotic changes of spermatogonium, for example, nuclear chromatin condensation, shrinkage, and detachment from Sertoli cells, which included many lysosomal granules. Leydig cells also showed evidence of chromatin condensation and significant induction of peroxisome proliferation. In conclusion, the potential causes of impaired testosterone biosynthesis might have been apoptosis of Leydig cells induced by direct toxicity of the hepatotoxin on testes or hypothalamopituitary dysfunction.

Concentration dependency in lead-inhibited steroidogenesis in MA-10 mouse Leydig tumor cells

Lead acetate (Pb) decreases the expression of steroidogenic acute regulatory (StAR) protein and the enzymatic activities of cytochrome P-450 side-chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in a concentration-dependent manner in Leydig cells at 2 h, the duration of submaximal inhibition. This study was undertaken at 3 h of Pb incubation to compare the effects at maximal metal inhibition of steroidogenesis. Quantitatively a 3-h Pb incubation with MA-10 cells resulted in higher decreases in human chorionic gonadotropin (hCG)-stimulated progesterone production, expression of StAR protein, and the activity of 3beta-HSD compared to 2 h. In contrast, lead inhibited dibutyryl cAMP (dbcAMP)-stimulated progesterone production but lacked this effect at 2 h. Surprisingly, Pb at 3 h of incubation did not affect P450scc enzyme activity, yet this enzymatic activity was inhibited at 2 h. Data indicate that incubation time is a factor in Pb-induced alterations in MA- 10 cell steroidogenesis.

Morphologic change and elevation of cortisol secretion in cultured human normal adrenocortical cells caused by mutant p21K-ras protein

In our previous study on the tumorigenesis of human functional adrenal tumors, we observed a high frequency of K-ras point mutations in clinical specimens. Furthermore, we cloned the mutated K-ras gene from the tumors and inserted it into vectors to transfect normal bovine adrenocortical cells to express the mutated K-ras gene. The mRNA level of steroidogenic enzymes such as cholesterol sidechain cleavage enzyme (P450SCC), 17alpha-hydroxylase/17,20-lyase (P450c17), and 3beta-hydroxysteroid dehydrogenase (3betaHSD) in the mutant K-ras stably transfected cells were elevated. Cultured normal adrenocortical cells from donors and patients with adrenocortical tumors were then transfected with mutant K-ras expression plasmids constructed from human adrenal tumors. Stable transfectants grew faster than normal cells. Additionally, morphologic change was observed in the transfected cells. Moreover, when the synthesis of hormones was analyzed, the mRNA of P450SCC, P450C17, and 3betaHSD was found to have increased, and the level of cortisol was 18 to 25 times that in control cells. The increased steroid hormone production in mutant K-ras-transfected cells was reversed by lovastatin, a pharmacologic inhibitor of p21ras function. These results, combined with previous reports of steroidogenic K-ras in bovine adrenocortical cells, suggest that the K-ras oncogene is involved in steroidogenesis in human adrenocortical cells.

Activation of cAMP-dependent protein kinase increases the protein level of steroidogenic factor-1

The orphan nuclear receptor steroidogenic factor 1 (SF-1) is an essential regulator of endocrine organogenesis, sexual differentiation, and steroidogenesis. SF-1 is a transcriptional regulator of cAMP responsive genes, but the exact mechanisms by which cAMP-dependent PKA modulates SF-1 dependent transcription leading to increased steroidogenic output have not been determined. In this report the effects of PKA activation on SF-1 in living cells have been examined by the use of full-length SF-1 cDNA fused to the cDNA encoding green fluorescent protein (GFP). The GFP-SF-1 fusion protein localized to the nucleus of both steroidogenic Y1 cells and nonsteroidogenic COS-1 cells, and the functional properties of wild-type SF-1 were conserved. When the catalytic subunit of PKA was coexpressed with GFP-SF-1, we observed that the fluorescence emission was markedly elevated. These findings were confirmed by Western blot analysis, showing that stimulation of PKA increased SF-1 protein levels. The PKA- induced expression of SF-1 protein was not accompanied by an increase in SF-1 mRNA levels. However, pulse-chase studies showed a decrease in SF-1 degradation rate in response to activation of PKA, indicating that PKA elevates the level of SF-1 by increasing the stability of SF-1 protein.

Effect of bone morphogenetic protein-7 on folliculogenesis and ovulation in the rat

We have previously established the presence of a functional bone morphogenetic protein (BMP) system in the ovary by demonstrating the expression of BMP ligands and receptors as well as novel cellular functions. Specifically, BMP-4 and BMP-7 are expressed in theca cells, and their receptors by granulosa cells. These BMPs enhanced and attenuated the stimulatory action of FSH on estradiol and progesterone production, respectively. To investigate the underlying mechanism of the differential regulation, we analyzed mRNA levels for key regulators in the steroid biosynthetic pathways by RNase protection assay. BMP-7 enhanced P450 aromatase (P450(arom)) but suppressed steroidogenic acute regulatory protein (StAR) mRNAs induced by FSH, whereas mRNAs encoding further-downstream steroidogenic enzymes, including P450 side-chain cleavage enzyme and 3beta-hydroxysteroid dehydrogenase, were not significantly altered. These findings suggest that BMP-7 stimulation and inhibition of P450(arom) and StAR mRNA expression, respectively, may play a role in the mechanisms underlying the differential regulation of estradiol and progesterone production. To establish the physiological relevance of BMP functions, we investigated the in vivo effects of injections of recombinant BMP-7 into the ovarian bursa of rats. Ovaries treated with BMP-7 had decreased numbers of primordial follicles, yet had increased numbers of primary, preantral, and antral follicles, suggesting that BMP-7 may act to facilitate the transition of follicles from the primordial stage to the pool of primary, preantral, and antral follicles. In this regard, we have also found that BMP-7 caused an increase in DNA synthesis and proliferation of granulosa cells from small antral follicles in vitro. In contrast to the stimulatory activity, BMP-7 exhibited pronounced inhibitory effects on ovulation rate and serum progesterone levels. These findings establish important new biological activities of BMP-7 in the context of ovarian physiology, including folliculogenesis and ovulation.

Minireview: sex differentiation

Mammalian sex differentiation is a hormone-dependent process in the male following the determination of a testis from the indifferent gonad through a cascade of genetic events. Female sex differentiation is not dependent on ovarian hormones, yet there is evidence that members of the Wnt family of developmental signaling molecules play a role in Müllerian duct development and in suppressing Leydig cell differentiation in the ovary. The testis induces male sex differentiation (including testis descent) through a time-dependent production of optimal concentrations of anti-Müllerian hormone, insulin-like factor(s) and androgens. Observations in several human syndromes of disordered fetal sex development corroborate findings in murine embryo studies, although there are exceptions in some gene knockout models. The ubiquitously expressed AR interacts in a ligand-dependent manner with coregulators to control the expression of androgen-responsive genes. Preliminary studies suggest the possibility of hormone resistance syndromes associated with coregulator dysfunction. Polymorphic variants in genes controlling androgen synthesis and action may modulate androgenic effects on sex differentiation.

Differential effects of agonists of aldosterone secretion on steroidogenic acute regulatory phosphorylation

The steroidogenic acute regulatory (StAR) protein mediates cholesterol transport within the mitochondria, and its phosphorylation is believed to be required for steroidogenesis. Increased extracellular potassium concentrations (K(+)), angiotensin II (AngII), and adrenocorticotropic hormone (ACTH) induce aldosterone secretion from bovine adrenal glomerulosa cells. We hypothesized that, although these agonists act via different signaling pathways, StAR phosphorylation should be common to their action. We studied the effects of K(+), AngII, and ACTH, at concentrations that yield comparable secretory responses, on StAR phosphorylation. All three agents induced significant increases in StAR phosphorylation although the response to ACTH was less than that of AngII and K(+). In cells stimulated with the protein kinase C (PKC) agonist 12-tetradecanoylphorbol 13-acetate (TPA), the Ca(2+) channel agonist BAY K8644, and the adenylate cyclase agonist forskolin, TPA caused a small but statistically significant increase in StAR phosphorylation while BAY K8644 and forskolin had no significant effect. Interestingly, the combination of TPA and BAY K8644 produced a larger increase in StAR phosphorylation than the agents alone. We conclude that in cultured bovine adrenal glomerulosa cells the PKC signaling pathway is most effective at inducing StAR phosphorylation but that there is no simple correlation between this event and aldosterone production.

Glucocorticoids protect against apoptosis induced by serum deprivation, cyclic adenosine 3',5'-monophosphate and p53 activation in immortalized human granulosa cells: involvement of Bcl-2

Glucocorticoid hormones are known to enhance gonadotropin/cAMP-induced steroidogenesis in rat and human granulosa cells. As glucocorticoids induce apoptosis in numerous cell types, we investigated the role of glucocorticoids in the control of apoptosis in immortalized human granulosa cells (HO-23) transfected with a temperature-sensitive mutant of p53 (Val(135)). When HO-23 were incubated with forskolin in the presence or absence of dexamethasone (Dex) at 32 or 37 C, progesterone production was higher by 4- and 8-fold in the presence of Dex at 37 or 32 C, respectively (P: < 0. 01). The expression of adrenodoxin (ADX), which is an intrinsic part of the cytochrome P450 side-chain cleavage enzyme system, remained the same in the presence or absence of Dex in forskolin-stimulated cells. Dex reduced apoptosis (to 33% of control) in cultures after activation of p53 by shifting the temperature from 37 to 32 C. Moreover, Dex suppressed apoptosis induced by serum deprivation (to 40% of control) or forskolin stimulation (to 28% and 40% at 37 and at 32 C, respectively). The protective effect of Dex on cAMP-, p53-, and serum deprivation-induced apoptosis was confirmed by both 4',6-diamido-2-phenylindole hydrochloride DNA staining and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling with an ED(50) of 7 nM Dex. Hydrocortisone showed a similar antiapoptotic effect. The protective effect of glucocorticoids against apoptosis was completely abolished by RU486 when cells were coincubated with 10 nM Dex and 10-100 nM RU486. The protection against apoptosis by glucocorticoid involved a sharp elevation in intracellular levels of Bcl-2 (3-7.6 fold; P: < 0.01). In contrast to the effect of Dex in the prevention of apoptosis in HO-23 granulosa cells, Dex dramatically stimulated apoptosis by 3-fold in LTR-6 myeloid leukemia cells expressing the same temperature-sensitive mutant (Val(135) p53) and the same amount of glucocorticoid receptor-alpha. Forskolin did not stimulate apoptosis when incubated with these cells. However, it augmented by 1.2-fold the p53-induced apoptosis in cells shifted from 37 to 32 C. Dex further enhanced apoptosis by 1.9-fold in p53-activated cultures (32 C). Incubation of the cells with Dex dramatically reduced Bcl-2 levels to 15% of control at 37 C (P: < 0.01) or 32 C in the presence or absence of forskolin (P: < 0.01). Our data suggest that glucocorticoids exert a protective effect against induced apoptosis in immortalized granulosa cells and a stimulatory effect on apoptosis in myeloid leukemia cells. Moreover, modulation of Bcl-2 levels plays an important role in mediating the glucocorticoid effect on cell survival. The opposite effect of glucocorticoids on Bcl-2 levels in the two cell lines may be due to the different ontogeneses of the two cell types: epithelial for granulosa cells vs. mesenchymal for myeloid cells studied in the present work.

Diametric effects of bacterial endotoxin lipopolysaccharide on adrenal and Leydig cell steroidogenic acute regulatory protein

Immune activation results in the activation of adrenal steroidogenesis and inhibition of gonadal steroidogenesis. Previous studies indicated that these effects were caused primarily by activation and suppression of the secretion of ACTH and LH, respectively. However, other evidence indicated a direct effect of the immune system on the gonads. In this study, serum testosterone, quantitated by RIA after lipopolysaccharide injection, showed a significant decrease within 2 h. Parallel measurement of serum LH showed no change. There were no differences in LH receptor or cAMP produced in Leydig cells between vehicle- and lipopolysaccharide-injected mice. The 30-kDa form of the steroidogenic acute regulatory (StAR) protein was quantitated, by Western blot, in Leydig cells and was found to decrease in a time-dependent manner. No change in StAR protein messenger RNA (mRNA) was detected by Northern analysis during this time, nor were any changes found in the levels of mRNA for the steroidogenic enzymes P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c17. In the adrenal, StAR protein was increased, as was StAR protein mRNA. No changes were observed in the levels of mRNA for P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c21. Thus, although the mechanisms of regulation differ, changes in the levels of StAR protein are a sensitive indicator of the steroidogenic capacity of these two tissues.

A trypsin-sensitive protein is required for utilization of exogenous cholesterol for pregnenolone synthesis by placental mitochondria

The utilization of cholesterol for steroid hormone synthesis by human placental mitochondria is poorly understood. The human placenta does not express the steroidogenic acute regulator protein, which is critical for cholesterol delivery to the cholesterol side chain cleavage system in adrenal and gonadal mitochondria. We explored the mechanism underlying cholesterol transport in human placental mitochondria by measuring its transformation into pregnenolone. Mitochondria of syncytiotrophoblast from human term placenta were isolated by centrifugation through a sucrose gradient. The synthesis of pregnenolone in the presence of exogenous cholesterol was increased two-fold in syncytiotrophoblast mitochondria. Treatment of mitochondria with trypsin prevented the increase in the synthesis of pregnenolone in the presence of exogenous cholesterol. However, when 22-OH cholesterol, a substrate that readily crosses membranes, was added, the trypsin-treated mitochondria synthesized increased amounts of pregnenolone. The trypsin-treated mitochondria were intact, since oxygen consumption, succinate dehydrogenase and the adenine nucleotide translocase activities were not significantly different from in untreated mitochondria. However, activity of NADH cytochrome c oxidoreductase, an outer mitochondrial membrane enzyme, was reduced in the trypsin-treated mitochondria, reflecting the selective degradation of proteins. In addition, SDS-PAGE analysis revealed the loss of a prominent 34 kDa band which proved to be a novel porin-like protein that binds to cholesterol. These results support our previous assumption that human placental mitochondria employ a novel protein(s)-mediated the mechanism to take up cholesterol for steroidogenesis.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Prostaglandin F(2alpha) induces a rapid decline in progesterone production and steroidogenic acute regulatory protein expression in isolated rat corpus luteum without altering messenger ribonucleic acid expression

With interest in steroidogenic acute regulatory protein (StAR) involvement in the luteolytic process, we studied changes in serum progesterone levels and the concomitant expression of StAR mRNA and protein (37-, 32-, and 30-kDa forms) in postovulatory Day 7 corpora lutea (CL) isolated from rats 1 h after injection with prostaglandin F(2alpha) (PGF(2alpha), n = 6) or saline (n = 6). Serum progesterone levels were determined by RIA, StAR and beta-actin mRNA expression by Northern analysis, and StAR and beta-actin protein expression by Western analysis. Adrenal, brain, and spleen from control animals were used as positive and negative controls for StAR expression. Scanning optical densitometry measurements were standardized by dividing the signal strength from each StAR autoradiogram lane by that from the corresponding beta-actin autoradiogram lane. ANOVA was used for significance testing, with alpha set at 0.05. The 37-, 32-, and 30-kDa forms of StAR protein were expressed in all adrenal samples, whereas only the 37- and 30-kDa forms were found in CL. Serum progesterone levels and expression of the 30-kDa and 37-kDa forms of the StAR protein in CL were all found to be significantly lower in the PGF(2alpha)-treated than the saline-treated group. StAR mRNA expression was not significantly different in the saline- and PGF(2alpha)-treated rats. The rapid decline in StAR protein expression that accompanies PGF(2alpha) induced luteolysis, therefore, does not result from significant decline in mRNA expression.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Regulation of steroidogenesis in jc-410, a stable cell line of porcine granulosa origin

We investigated the regulation of steroidogenesis in a cell line of porcine granulosa origin, JC-410. Cells responded to the protein kinase-A activators, cholera toxin and forskolin, with increased accumulation of intracellular cAMP. Histochemically, cells were shown to contain 3beta-HSD, the enzyme which converts pregnenolone to progesterone. The JC-410 cells produced progesterone and responded to the protein kinase-A activators with an increase in progesterone synthesis. Progesterone levels were also increased by 25-hydroxycholesterol, pregnenolone, estradiol and androstenedione. Follicle-stimulating hormone and luteinizing hormone had no effect on cAMP or progesterone accumulation. Androstenedione was required for the synthesis of estradiol by JC-410 cells. Steady-state levels of mRNA for the steroidogenic enzymes 3beta-HSD and P450scc were increased by treatment with cholera toxin, whereas P450arom was not changed. These cells express the steroidogenic enzymes genes in a similar fashion to primary cultures of porcine granulosa cells. The JC-410 cells may represent a valuable model to study second messenger regulation and the molecular mechanisms involved in steroidogenesis in granulosa cells.

The role of arachidonic acid on LH-stimulated steroidogenesis and steroidogenic acute regulatory protein accumulation in MA-10 mouse Leydig tumor cells

Metabolic pathways leading to the production of arachidonic acid (AA) and its metabolites have been reported to have modulatory effects on steroidogenesis in a number of cell types. To examine the importance of the arachidonic acid pathway in steroid production and steroidogenic acute regulatory (StAR) protein expression, luteinizing hormones (LH) or N6-2-o-dibutyryl-adenosine-3:5-cyclic monophosphate-(Bt2cAMP) stimulated MA-10 mouse Leydig tumor cells were treated with various concentrations of quinacrine (an inhibitor of arachidonic acid production). Incubation of the cells with quinacrine resulted in dose-dependent decreases in steroid production and StAR protein. Twenty micromolars quinacrine inhibited 92 and 91% of LH-induced progesterone and StAR protein, respectively, and 98 and 90% of Bt2cAMP-induced progesterone and StAR protein. Reversal of this inhibition was obtained by incubation of quinacrine-treated cells with various levels of AA, which resulted in a dose-dependent increase in both steroid and StAR protein levels. Two hundred micromolars of AA rescued 57 and 60% of the LH-induced steroid production and StAR protein, respectively, and 52 and 89% of Bt2cAMP-induced steroid production and StAR protein. These results suggest that the effect of AA on LH- and cAMP-stimulated steroidogenesis is associated with the modulation of StAR protein expression.

Role of proteoglycans on testosterone synthesis by purified Leydig cells from immature and mature rats

In order to characterize an involvement of proteoglycans (PG) in the regulation of Leydig cell function, we have examined the effects of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis and para-nitrophenyl-beta-D-galactoside (PNPG), an inefficient structural analogue, on testosterone production by purified Leydig cells from immature and mature rats, in the presence or not of various concentrations of hCG during 24 h. Whatever the age, the addition of PNPX induces a decrease of [35S] and [3H] incorporations into cell layer associated-PG; these latter being less numerous (-50 and -25%, respectively in immature and mature rat), and less sulfated (-40%) when compared to control Leydig cells. In immature Leydig cells, the inhibition of PG synthesis decreases both the basal and weakly stimulable-hCG or -(Bu)2cAMP or -LH testosterone synthesis. In mature Leydig cells, the PG inhibition has no effect on testosterone production both in the absence of hCG and in the presence of weak amounts of hCG but increases it in the presence of subsaturating hCG concentrations. Whatever the age, the inhibition of PG synthesis is ineffective in the presence of saturating amounts of either hCG or (Bu)2cAMP. These effects are maintained in the presence of MIX, PMA, but are not observed in the presence of 22R-hydroxycholesterol. Therefore, our results suggest that in rat Leydig cells, the inhibition of PG synthesis affects the signal transduction at a step distal to cyclic AMP and more precisely, the cholesterol supply to the mitochondria by acting on its cellular distribution (free and esterified cholesterol).

Mechanisms of insulin-like growth factor I augmentation of follicle-stimulating hormone-induced porcine steroidogenic acute regulatory protein gene promoter activity in granulosa cells

Insulin-like growth factor I (IGF-I) and the gonadotropin, FSH, can synergize to stimulate progesterone production in primary cultures of maturing human, rat, and pig granulosa cells. These trophic hormones act by increasing the activity and production of proteins and their gene transcripts essential to sterol uptake, delivery, and utilization in steroidogenesis. We previously observed that FSH and IGF-I interact synergistically to promote the accumulation of steroidogenic acute regulatory protein (StAR) messenger RNA and protein in granulosa cells. Here we investigate potential mechanisms of IGF-I synergy with FSH and the protein kinase A (PKA) pathway in activating the porcine StAR gene promoter. To this end, we first cloned 1423 bp of the porcine StAR promoter upstream of the transcriptional start site using PCR and created 5'-deletional constructs coupled to a cytoplasmically targeted firefly luciferase reporter gene. FSH, 8-bromo-cAMP, and transient transfection of the protein kinase A (PKA) catalytic subunit (driven by the Rous sarcoma virus promoter) were used to activate the PKA effector pathway. All three agonists alone stimulated StAR promoter-driven luciferase activity in primary cultures of granulosa cells after 4-h treatment. IGF-I significantly augmented PKA pathway agonist activation of the StAR promoter, whereas IGF-I had no effect alone. Binding experiments with 125I-labeled ovine FSH-20 in IGF-I (100 ng/ml)-treated granulosa cells showed that FSH binding affinity and receptor number were unchanged by IGF-I treatment. However, IGF-I augmented FSH-stimulated, but not forskolin-stimulated, cAMP accumulation. Analysis of 5'-deletion constructs of the StAR promoter revealed three regions of stimulatory activity within the -139-bp fragment upstream of the transcriptional start site as well as another potentially inhibitory region upstream (-1115 to 905). Elimination of the putative SF-1 site (-48 to -41) virtually abolished StAR promoter responsiveness. In summary, our data indicate that IGF-I can act via two post FSH-binding mechanisms to augment FSH/PKA pathway-mediated StAR gene promoter transactivation: at the level of cAMP accumulation and distal to cAMP production and PKA activation.

The acute regulation of mineralocorticoid biosynthesis: scenarios for the StAR system

The zona glomerulosa cell of the adrenal cortex produces mineralocorticoids in response to physiological stimuli (angiotensin II and extracellular K(+)) activating the Ca(2+) messenger system. The mechanisms underlying the generation of the Ca(2+) signal have been analyzed extensively and recent developments have contributed to bridging the gap between intracellular signals and activation of the biological function. This article summarizes the current knowledge on the intracellular targets of the Ca(2+) messenger, obtained mainly in bovine glomerulosa cells. Ca(2+) appears to exert a dual effect, both at the intramitochondrial level and at the nuclear level, where it activates steroidogenic acute regulatory protein (StAR) gene transcription.

Effect of truncated forms of the steroidogenic acute regulatory protein on intramitochondrial cholesterol transfer

It has been proposed that the steroidogenic acute regulatory (StAR) protein controls hormone-stimulated steroid production by mediating cholesterol transfer to the mitochondrial inner membrane. This study was conducted to determine the effect of wild-type StAR and several modified forms of StAR on intramitochondrial cholesterol transfer. Forty-seven N-terminal or 28 C-terminal amino acids of the StAR protein were removed, and COS-1 cells were transfected with pCMV vector only, wild-type StAR, N-47, or the C-28 constructs. Lysates from the transfected COS-1 cells were then incubated with mitochondria from MA-10 mouse Leydig tumor cells that were preloaded with [3H]cholesterol. After incubation, mitochondria were collected and fractionated on sucrose gradients into outer membranes, inner membranes, and membrane contact sites, and [3H]cholesterol content was determined in each membrane fraction. Incubation of MA-10 mitochondria with wild-type StAR containing cell lysate resulted in a significant 34.9% increase in [3H]cholesterol content in contact sites and a significant 32.8% increase in inner mitochondrial membranes. Incubations with cell lysate containing N-47 StAR protein also resulted in a 16.4% increase in [3H]cholesterol in contact sites and a significant 26.1% increase in the inner membrane fraction. In contrast, incubation with the C-28 StAR protein had no effect on cholesterol transfer. The cholesterol-transferring activity of the N-47 truncation, in contrast to that of the C-28 mutant, was corroborated when COS-1 cells were cotransfected with F2 vector (containing cytochrome P450 side-chain cleavage enzyme, ferridoxin, and ferridoxin reductase) and either pCMV empty vector or the complementary DNAs of wild-type StAR, N-47 StAR, or C-28 StAR. Pregnenolone production was significantly increased in both wild-type and N-47-transfected cells, whereas that in C-28-transfected cells was similar to the control value. Finally, immunolocalization studies with confocal image and electron microscopy were performed to determine the cellular location of StAR and its truncated forms in transfected COS-1 cells. The results showed that wild-type and most of the C-28 StAR protein were imported into the mitochondria, whereas most of N-47 protein remained in the cytosol. These studies demonstrate a direct effect of StAR protein on cholesterol transfer to the inner mitochondrial membrane, that StAR need not enter the mitochondria to produce this transfer, and the importance of the C-terminus of StAR in this process.

Atrial natriuretic peptide inhibits calcium-induced steroidogenic acute regulatory protein gene transcription in adrenal glomerulosa cells

Atrial natriuretic peptide (ANP) is a potent inhibitor of mineralocorticoid synthesis induced in adrenal glomerulosa cells by physiological agonists activating the calcium messenger system, such as angiotensin II (Ang II) and potassium ion (K+). While the role of calcium in mediating Ang II- and K(+)-induced aldosterone production is clearly established, the mechanisms leading to blockade of this steroidogenic response by ANP remain obscure. We have used bovine adrenal zona glomerulosa cells in primary culture, in which an activation of the calcium messenger system was mimicked by a 2-h exposure to an intracellular high-calcium clamp. The effect of ANP was studied on the following parameters of the steroidogenic pathway: 1) pregnenolone and aldosterone production; 2) changes in cytosolic ([Ca2+]c) and mitochondrial ([Ca2+]m) Ca2+ concentrations, as assessed with targeted recombinant aequorin; 3) cholesterol content in outer mitochondrial membranes (OM), contact sites (CS), and inner membranes (IM); 4) steroidogenic acute regulatory (StAR) protein import into mitochondria by Western blot analysis; 5) StAR protein synthesis, as determined by [35S]methionine incorporation, immunoprecipitation, and SDS-PAGE; 6) StAR mRNA levels by Northern blot analysis with a StAR cDNA; 7) StAR gene transcription by nuclear run-on analysis. While clamping Ca2+ at 950 nM raised pregnenolone output 3.5-fold and aldosterone output 3-fold, ANP prevented these responses with an IC50 of 1 nM and a maximal effect of 90% inhibition at 10 nM. In contrast, ANP did not affect the [Ca2+]c or [Ca2+]m changes occurring under Ca2+ clamp or Ang II stimulation in glomerulosa cells. The accumulation of cholesterol content in CS (139.7 +/- 10.7% of control) observed under high-Ca2+ clamp was prevented by 10 nM ANP (92.4 +/- 4% of control). Similarly, while Ca2+ induced a marked accumulation of StAR protein in mitochondria of glomerulosa cells to 218 +/- 44% (n = 3) of controls, the presence of ANP led to a blockade of StAR protein mitochondrial import (113.3 +/- 15.0%). This effect was due to a complete suppression of the increased [35S]methionine incorporation into StAR protein that occurred under Ca2+ clamp (94.5 +/- 12.8% vs. 167.5 +/- 17.3%, n = 3). Furthermore, while the high-Ca2+ clamp significantly increased StAR mRNA levels to 188.5 +/- 8.4 of controls (n = 4), ANP completely prevented this response. Nuclear run-on analysis showed that increases in intracellular Ca2+ resulted in transcriptional induction of the StAR gene and that ANP inhibited this process. These results demonstrate that Ca2+ exerts a transcriptional control on StAR protein expression and that ANP appears to elicit its inhibitory effect on aldosterone biosynthesis by acting as a negative physiological regulator of StAR gene expression.

Effects of chronic exposure to PCBs on cytochrome P450 systems and steroidogenesis in liver and testis of bulls (Bos taurus)

Effects of chronic exposure to PCBs on the microsomal cytochrome P450 (CYP) enzymes in liver and testis of bulls (Bos taurus) were determined by comparing the constitutive and PCB-induced alkoxyresorufin O-dealkylase and testosterone hydroxylase activities. Specific inductions of the prevailing hepatic ethoxyresorufin O-deethylation and 6 beta-hydroxylation of testosterone are suggestive of the induction of CYP1A1 and CYP3A-like enzymes by PCBs. A high level of PCB-inducible androstenedione formation was also found. The hepatic CYP2B activities (i.e. pentoxyresorufin O-depentylase and testosterone 16 beta-hydroxylase) and CYP2C11-like testosterone 2 alpha-hydroxylase were increased only weakly. The testicular microsomal CYP activities were non-specifically reduced by the PCB exposure, except for the androstenedione formation and 16 beta-hydroxylation of testosterone. The inhibition of the activity of mitochondrial CYP11A, as the rate-limiting enzyme of steroidogenesis measured with resorufin 3 beta-hydroxy-22,23-bisnor-5-cholenyl ether as the fluorogenic substrate, exceeded 50% in testes of the PCB-contaminated bulls. The latter activity as well as the hepatic testosterone 6 beta-hydroxylation and hepatic and testicular androstenedione formation may significantly contribute to the decrease in testosterone levels after the PCB intake.

Steroid regulation during apoptosis of ovarian follicular cells

In each estrous cycle, only one follicle, the dominant follicle, reaches full maturation while the other recruited follicles become atretic in a process characteristic of programmed cell death. Moreover, the old corpus luteum formed in a previous cycle undergoes luteolysis by a mechanism also characteristic of programmed cell death. Granulosa cells comprise the largest cell population of the ovarian follicle and are the main source of estradiol and progesterone in the ovary. Their cyclic nature of differentiation and death determines the cyclic secretion of female sex hormones and therefore serve as an excellent model for steroid regulation during apoptosis. The characteristics of granulosa cell apoptosis, as in other cell types, are cell membrane blebbing, DNA degradation and protease activation. In addition, there are specific characteristics of steroidogenic granulosa cell apoptosis, as follows: 1) The trigger for apoptosis may be exerted by different effectors and signal transduction mechanisms during follicle development. For example, tumor necrosis factor (TNF) may trigger granulosa cell apoptosis at early stage of follicular development, while cAMP/p53 signals may trigger this process only in mature preovulatory granulosa cells. 2) cross-talk between paracrine and endocrine signals, and between death genes and tumor suppressor genes, may determine the fate of the granulosa cell. 3) in the mature follicle the follicular basement membrane plays an important role in transmitting survival signals and in prevention of apoptosis. 4) during the initial steps of apoptosis, steroidogenesis may be increased due to clustering of the steroidogenic organelles in the perinuclear region and their exclusion from the apoptotic blebs. 5) Actin cytoskeleton reorganization plays an important role in this compartmentalization as well as in transmitting survival signals exerted by basement membrane, laminin and growth factors which activate tyrosine kinase receptors.

Hormone and prostaglandin F2 alpha regulation of messenger ribonucleic acid encoding steroidogenic acute regulatory protein in human corpora lutea

Steroidogenic acute regulatory (StAR) protein mediates the rapid increase in steroid hormone biosynthesis in response to tropic hormones by facilitating transport of cholesterol into the inner mitochondrial membrane. Although our laboratory has recently reported on the hormonal regulation of StAR mRNA in the rat ovary, the same regulation in the human corpus luteum requires analysis. To this end, a human StAR complementary DNA (cDNA) probe of 858 bp was generated using reverse transcriptase-PCR and RNA from human corpora lutea. The StAR sequence was confirmed by dideoxy chain-termination sequence analysis. Northern blot analysis using the StAR cDNA probe on human corpora lutea mRNA showed that the probe hybridized to a major 1.6-kb transcript and a minor 4.4-kb transcript. Examination of corpora lutea of different luteal phases revealed that the basal expression of the 1.6-kb transcript was significantly more abundant in the early (days 15-19) luteal phase than in the middle (days 20-23) or late (days 24-28) phases. To examine the hormonal regulation of StAR mRNA, corpora lutea were treated in vitro with increasing concentrations of human chorionic gonadotropin (hCG) or prostaglandin F2 alpha (PGF2 alpha). Following hCG stimulation, both 1.6- and 4.4-kb StAR transcripts were increased. A statistically significant increase of 2.2- and 1.8-fold in the 1.6-kb transcript was seen with hCG concentrations of 50 and 100 mIU/mL, respectively. This increase was coupled with a significant elevation in media progesterone levels. In contrast, PGF2 alpha treatment significantly decreased both StAR messenger ribonucleic acid (mRNA) expression and media progesterone levels at concentrations of 500 and 5000 ng/mL. This investigation demonstrated that StAR mRNA is regulated by tropic hormones and prostaglandins in the human corpus luteum. The parallel change in StAR mRNA in conjunction with a change in progesterone levels further supports StAR's putative role in the regulation of steroidogenesis.

Diagnosis and management of congenital adrenal hyperplasia

Congenital adrenal hyperplasia is a family of inborn errors of steroidogenesis, each characterized by a specific enzyme deficiency that impairs cortisol production by the adrenal cortex, and can lead to sexual ambiguity in both genetic males and females. The enzymes most often affected are 21-hydroxylase, 11 beta-hydroxylase, and 3 beta-hydroxysteroid dehydrogenase, and less often, 17 alpha-hydroxylase/17, 20-lyase and cholesterol desmolase. Decreased production of cortisol results in increased pituitary secretion of adrenocorticotropic hormone. The elevated adrenocorticotropic hormone stimulates both the accumulation of precursor steroids in the impeded pathways and excessive steroid synthesis in other adrenal biosynthetic pathways unaffected by the enzyme deficiency. Correct identification of the enzyme affected is achieved by the observation of clinical syndromes reflecting distinct hormonal patterns, and it is measured quantitatively as low levels of cortisol and other adrenal steroids, as well as increased levels of steroids proximal to the blocked step. Many of the corresponding genes for the described enzymes have been isolated and characterized, and specific mutations causing many cases of congenital adrenal hyperplasia have been identified. These advances have important implications for early prenatal diagnosis and prenatal treatment.

Transforming growth factor beta1 decreases cholesterol supply to mitochondria via repression of steroidogenic acute regulatory protein expression

Transforming growth factor-betas (TGF-betas) constitute a family of dimeric proteins that affect growth and differentiation of many cell types. TGF-beta1 has also been proposed to be an autocrine regulator of adrenocortical steroidogenesis, acting mainly by decreasing the expression of cytochrome P450c17. Here, we demonstrate that TGF-beta1 has a second target in bovine adrenocortical cells, namely the steroidogenic acute regulatory protein (StAR). Indeed, supplying cells with steroid precursors revealed that TGF-beta1 inhibited two steps in the steroid synthesis pathway, one prior to pregnenolone production and another corresponding to P450c17. More specifically, TGF-beta1 inhibited pregnenolone production but neither the conversion of 25-hydroxycholesterol to pregnenolone nor P450scc activity. Thus, TGF-beta1 must decrease the cholesterol supply to P450scc. We therefore examined the effect of TGF-beta1 on the expression of StAR, a mitochondrial protein implicated in intramitochondrial cholesterol transport. TGF-beta1 decreased the steady state level of StAR mRNA in a time- and concentration-dependent manner. This inhibition occurs at the level of StAR transcription and depends on RNA and protein synthesis. It is likely that the TGF-beta1-induced decrease of StAR expression that we report here may be expanded to other steroidogenic cells in which a decrease of cholesterol accessibility to P450scc by TGF-beta1 has been hypothesized.

Spatio-temporal expression patterns of steroidogenic acute regulatory protein (StAR) during follicular development in the rat ovary

The steroidogenic acute regulatory protein (StAR) is a vital mitochondrial protein that is indispensable for the synthesis of steroid hormones in the steroidogenic cells of the adrenal cortex and the gonads. Recent studies have shown that StAR enhances the conversion of the substrate for all steroid hormones, cholesterol, into pregnenolone, probably by facilitating cholesterol entry into the inner compartment of the mitochondria where the steroidogenic cytochrome P450scc complex resides. To study the potential of StAR to affect ovarian steroidogenesis during follicular development, we examined the time-dependent expression of StAR protein and messenger RNA in PMSG/human CG (hCG)-treated immature rats. Western blot analyses and immunohistochemical and RT-PCR methodologies have revealed a biphasic expression of StAR in the ovaries responding to hormones. The first peak of StAR expression was generated by PMSG administration and lasted for 24 h. Furthermore, it was restricted to the entire network of the ovarian secondary interstitial tissue, as well as to a fewer scattered theca-interna cells. The second burst of StAR expression was observed in response to the LH surge, as simulated by hCG. This time, StAR was expressed in the entire theca-interna and interstitial tissue, as well as in those granulosa cells that were confined to periovulatory follicles. Immunoelectron microscopy studies revealed the over 90% of StAR antigenic sites are localized in the inner compartments of the mitochondrion, suggesting a rapid removal of StAR precursor from the mitochondrial surface, where it is believed to exert its activity. Altogether, our observations portray dynamic acute alterations of StAR expression during the process of follicular maturation in this animal model. Furthermore, if StAR indeed determines steroidogenic capacities in the ovary, our findings imply that, in immature rats undergoing hormonally induced first ovulation: 1) the early phases of follicular development are supported by androgen production originating from nonfollicular cells; 2) estrogen production in the granulosa cells of Graafian follicles is nourished by a submaximal androgenic output in the theca-interstitial compartments of the ovary.

Corticotropin-releasing hormone (CRH) inhibits steroid biosynthesis by cultured human granulosa-lutein cells in a CRH and interleukin-1 receptor-mediated fashion

The presence of immunoreactive CRH was recently demonstrated in human ovaries. CRH immunoreactivity was localized by immunohistochemistry in the cytoplasm of thecal cells surrounding the ovarian follicles, in luteinized cells of the stroma, and in large granulosa-derived luteinized cells of developing corpora lutea. Also, CRH and its receptors were identified in Leydig cells of the testis where CRH was shown to inhibit testosterone biosynthesis. To examine the role of CRH in the ovary, we studied its effect on estradiol (E2) and progesterone (P4) release by human granulosa cells obtained from women undergoing in vitro fertilization for male factor infertility or uni- or bilateral tubal impatency. In all subjects, superovulation was induced by treatment with gonadotropins. The effects of graded doses of ovine CRH (10[-11]-10[-6] mol/liter) were evaluated in the conditioned medium obtained after 24 h incubation of the cells. All CRH concentrations employed except for the lowest one (10[-11] mol/liter) caused a significant decrease of media E2 and P4 levels. Maximal inhibition for both E2 and P4 production was obtained by 10[-6] mol/liter CRH concentration, which decreased hormone production by 39% and 34%, respectively. The alpha-helical CRH9-41 antagonist at 10(-6) and 10(-7) mol/liter blocked the suppressive effect of 10(-9) mol/liter CRH on both E2 and P4 secretion, while it had no effect when added to the culture media without CRH. Since interleukin (IL-1)-1 mediates certain actions of CRH on leukocytes, we examined whether the CRH effect on ovarian steroidogenesis was IL-1-mediated. Interleukin-1 receptor antagonist at 10(-7) and 10(-6) mol/liter blocked the inhibitory effects of CRH on E2 and P4 secretion, while it had no effect in the absence of CRH. In conclusion, CRH exerts a CRH- and IL-1 receptor-mediated inhibitory effect on ovarian steroidogenesis and might be actively involved in the still enigmatic processes of follicular atresia and luteolysis.

Peripheral-type benzodiazepine receptors

1. The pharmacological effects of benzodiazepines are mediated through a class of recognition sites associated with the gamma-aminobutyric acid A receptor. A second class of benzodiazepine binding sites is found in virtually all mammalian peripheral tissues and is therefore called the peripheral type benzodiazepine receptor (PBR). 2. The first section of this review describes the tissue and subcellular distribution of the PBR in mammalian tissues and analyzes its many putative endogenous ligands. 3. The next section deals with the pharmacological, structural and molecular characterization of the PBR that has taken place in the past few years. 4. The final section describes the possible physiological role(s) of the PBR and identifies future work that would help deepen our understanding of the PBR and its function.

Leydig cell steroidogenesis in aging rats

Recent studies from our and other laboratories have shown that Leydig cells, the testicular cells responsible for testosterone production; become steroidogenically hypofunctional with age. Herein we review some of what we now know about the mechanisms by which this occurs, and some among the many remaining uncertainties in our understanding of Leydig cell aging. To help shed light on how Leydig cells age, we also briefly discuss the regulation of Leydig cell differentiation during puberty and of Leydig cell function in adult animals.

Submitochondrial distribution of three key steroidogenic proteins (steroidogenic acute regulatory protein and cytochrome p450scc and 3beta-hydroxysteroid dehydrogenase isomerase enzymes) upon stimulation by intracellular calcium in adrenal glomerulosa cells

In adrenal glomerulosa cells, angiotensin II (Ang II) and potassium stimulate aldosterone synthesis through activation of the calcium messenger system. The rate-limiting step in steroidogenesis is the transfer of cholesterol to the inner mitochondrial membrane. This transfer is believed to depend upon the presence of the steroidogenic acute regulatory (StAR) protein. The aim of this study was 1) to examine the effect of changes in cytosolic free calcium concentration and of Ang II on intramitochondrial cholesterol and 2) to study the distribution of StAR protein in submitochondrial fractions during activation by Ca2+ and Ang II. To this end, freshly prepared bovine zona glomerulosa cells were submitted to a high cytosolic Ca2+ clamp (600 nM) or stimulated with Ang II (10 nM) for 2 h. Mitochondria were isolated and subfractionated into outer membranes, inner membranes (IM), and contact sites (CS). Stimulation of intact cells with Ca2+ or Ang II led to a marked, cycloheximide-sensitive increase in cholesterol in CS (to 143 +/- 3. 2 and 151.1 +/- 18.1% of controls, respectively) and in IM (to 119 +/- 5.1 and 124.5 +/- 6.5% of controls, respectively). Western blot analysis revealed a cycloheximide-sensitive increase in StAR protein in mitochondrial extracts of Ca2+-clamped glomerulosa cells (to 159 +/- 23% of controls). In submitochondrial fractions, there was a selective accumulation of StAR protein in IM following stimulation with Ca2+ (228 +/- 50%). Similarly, Ang II increased StAR protein in IM, and this effect was prevented by cycloheximide. In contrast, neither Ca2+ nor Ang II had any effect on the submitochondrial distribution of cytochrome P450scc and 3beta-hydroxysteroid dehydrogenase isomerase. The intramitochondrial presence of the latter enzyme was further confirmed by immunogold staining in rat adrenal fasciculata cells and by immunoblot analysis in MA-10 mouse testicular Leydig cells. These findings demonstrate that under acute stimulation with Ca2+-mobilizing agents, newly synthesized StAR protein accumulates in IM after transiting through CS. Moreover, our results suggest that the import of StAR protein into IM may be associated with cholesterol transfer, thus promoting precursor supply to the two first enzymes of the steroidogenic cascade within the mitochondria and thereby activating mineralocorticoid synthesis.

Nucleotide sequence of rat steroidogenic acute regulatory protein complementary DNA

The steroidogenic acute regulatory (StAR) protein is a key regulator for the steroidogenesis in acute response to trophic hormone. A rat complementary DNA of the StAR protein was cloned and its complete nucleotide sequence was determined. The deduced amino acid sequence of the clone has an additional 86 amino acid stretch at amino terminus when it was compared with those sequences in other species. The other part of the amino acid sequence has 94% identity to mouse StAR protein sequence. Three transcripts (1.3 kb, 1.6 kb, and 3.5 kb) which are hybridizing to the clone were detected in testis, ovary and adrenal gland. When the cDNA was expressed in COS1 cells, 30 kDa and 47 kDa proteins specific to the anti-StAR antibody were detected.

Control of cholesterol access to cytochrome P450scc in rat adrenal cells mediated by regulation of the steroidogenic acute regulatory protein

Cholesterol conversion to pregnenolone by cytochrome P450scc in steroidogenic cells, including those of the adrenal cortex, is determined by hormonal control of cholesterol availability. Intramitochondrial cholesterol movement to P450scc, which retains hormonal activation in isolated mitochondria, is apparently dependent on peripheral benzodiazepine receptor and the recently cloned steroidogenic acute regulatory (StAR) protein. In rat adrenal cells, StAR is formed as a 37-kDa precursor that is transferred to the mitochondrial inner membrane following phosphorylation by hormonally activated protein kinase A, and processed to multiple forms, some of which turn over very rapidly. In bovine cells, StAR undergoes three modifications forming a set of eight proteins seen in both glomerulosa and fasciculata cells. In the former, cyclic AMP and angiotensin II each decrease two forms and elevate six forms. Significantly, the major change seen after activation may not involve phosphorylation of StAR. Cholesterol transfer across mitochondrial membranes is also activated in isolated mitochondria by GTP and low concentrations of Ca2+, apparently prior to activation by StAR. Depletion of StAR by cycloheximide inhibits cholesterol transfer but is overcome by uptake of Ca2+ into the matrix. This activation of cellular cholesterol transport is sustained in adrenal cells permeabilized by Streptolysin O. In rat adrenal cells cAMP elevates 3.5- and 1.6-kb mRNA, hybridized by a 1.0-kb StAR cDNA. A 3.5-kb rat adrenal cDNA that encodes all except the 5' end of the longest StAR mRNA has been characterized. The corresponding gene sequence is distributed across seven exons. The shorter mRNA may arise from polyadenylation signals early in exon 7. However, the 3.5-kb mRNA comprises 80-90% of untreated rat adrenal StAR mRNA and may therefore provide the prime source for in vivo translation of StAR protein.

Partial sequencing of the rat steroidogenic acute regulatory protein message from immortalized granulosa cells: regulation by gonadotropins and isoproterenol

Steroidogenic acute regulatory protein (StAR), a 30-kDa protein involved in the transport of cholesterol to inner mitochondrial membrane during stimulation of steroid hormone biosynthesis, has recently been cloned from human adrenals and MA-10 mouse Leydig tumor cells. We examined the regulation of StAR mRNA accumulation upon induction of steroidogenesis in immortalized rat granulosa cells. Granulosa cells were transfected with SV40 DNA alone (POGS5); with SV40 DNA and Ha-ras oncogene (POGRS1); with SV40 DNA, Ha-ras oncogene and LH/CG receptor (GLHR15) or with FSH receptor (GFSHR17) or with the beta 2-adrenergic receptor (G beta 2AR13) expression plasmids. Cells were cultured to confluency and then stimulated for 24 h with oFSH (4 nM), hCG (2.4 nM), isoproterenol (10 microM) or forskolin (50 microM). By quantitative RT-PCR, StAR mRNA was undetectable in non-steroidogenic cells (transfected with SV40 DNA alone, POGS5) either in the presence or in the absence of forskolin. In contrast, variable amount of the message was detected in all steroidogenic cell lines cotransfected with SV40 DNA and Ha-ras. Moreover, an increase in the StAR mRNA expression was evident in all steroidogenic cells upon stimulation with their respective agonists, concomitantly with enhanced progesterone production. The RT-PCR product was sequenced and the 379 base pairs of rat StAR were found to be 93% and 86% identical to mouse and human cDNA, respectively. The deduced 126 amino acid sequence was 95%, 88% and 88% identical to the mouse, human and bovine deduced protein sequences. We conclude that StAR message is expressed only in the steroidogenic rat granulosa cells and can be upregulated by FSH, hCG, isoproterenol and forskolin in the appropriate cell lines. In addition, we find that the rat StAR cDNA exhibit a high degree of homology with the mouse and human sequences.

Prostaglandin F2α reduces steroidogenic acute regulatory (StAR) protein messenger ribonucleic acid expression in the rat ovary

Steroid biosynthesis begins with the enzymatic conversion of cholesterol to pregnenolone. This reaction is catalyzed by the cytochrome P450 side-chain cleavage enzyme (P450scc), which is located on the matrix side of the inner mitochondrial membrane. Although the rate-limiting enzymatic step in steroidogenesis is the conversion of cholesterol to pregnenolone by the side-chain cleavage enzyme, the true rate-limiting step in this process is the delivery of cholesterol to the inner mitochondrial membrane. Steroidogenic acute regulatory (StAR) protein is thought to mediate the rapid increase in steroid hormone biosynthesis in response to tropic hormones by facilitating cholesterol transport to the inner mitochondrial membrane. Cholesterol transport across the inner mitochondrial membrane has also been implicated as the target for prostaglandin F2α's (PGF2α) antisteroidogenic activity. Since cholesterol delivery to the P450scc is a rapidly regulated step in steroidogenesis, StAR mRNA levels were examined after the administration of a luteolytic injection of PGF2α. The results of this investigation revealed that both major StAR RNA transcripts were decreased in the ovary, 10 d after ovulation, following PGF2α administration. Serum progesterone levels were decreased following PGF2α administration in parallel with the decreased expression of StAR. Following PGF2α treatment, ovarian StAR transcripts at 3.4 and 1.6 kb were reduced 4-fold (p<0.01) and 2.5-fold (p<0.025), respectively, after 4 h. Ovarian P450scc mRNA levels were also reduced (70%) 4 h after PGF2α injection. Time course experiments following PGF2α administration showed a significant decrease in StAR expression as early as 30 min (p<0.02) following injection. In contrast to StAR's expression after PGF2α administration, StAR mRNA levels were elevated in response to human chorionic gonadotropin (hCG) 3 h postinjection. Administration of PGF2α followed by hCG injection effectively blocked induction of StAR expression. StAR mRNA levels were reduced 1.5-fold relative to control animals and 3.5-fold relative to the hCG-treated animals (p<0.05). The levels of serum progesterone paralleled the change in ovarian StAR mRNA in all experiments. This study provides the first evidence that StAR mRNA expression is mediated by prostaglandins in the rat ovary further supporting its important role in the regulation of steroid hormone biosynthesis.

Differential incorporation of cholesterol and cholesterol derivatives into ecdysteroids by the larval ring glands and adult ovaries of Drosophila melanogaster: a putative explanation for the l(3)ecd1 mutation

Studies in vitro revealed that intact ring glands of Drosophila melanogaster convert tritiated cholesterol (C) and 25-hydroxycholesterol (25C) via 7-dehydrocholesterol (7dC) and 7-dehydro-25-hydroxycholesterol (7d25C), respectively, to ecdysone (E) and 2-deoxyecdysone (2dE), while both intact and homogenized ovaries synthesize only 2dE from these precursors. Emulsified 7d25C was incorporated directly into ecdysteroids by these tissue preparations at a much greater rate than was 7d25C made in situ from 25C. To probe the basis of the biochemical defect in the ecdysteroid deficient conditional mutant ecdysoneless (ecd1), the differential incorporation into ecdysteroids of C (via 7dC), and particularly of 25C (via 7d25C), was measured relative to that observed after the incubation of 7d25C directly with both wild type and mutant tissues in vitro at 30 degrees C, the restrictive temperature. Both C and 25C were equally 7,8-dehydrogenated in situ to 7dC or 7d25C, respectively, by both wild type and mutant tissues at 30 degrees C. However, the rate of subsequent conversion of either of these delta 5,7-sterol intermediates synthesized in situ to ecdysteroids was reduced an average of 50% in the mutant tissues relative to the wild type. Yet, when emulsified 7d25C was incubated directly with either the wild type or mutant tissues at the restrictive temperature, the amplified rate of conversion of the freely available 7d25C to ecdysteroid by these tissues was identical. These data suggest that the defect in ecd1 tissue-mediated ecdysteroidogenesis does not involve a "hit" on any of the enzymes involved in either the 7,8-dehydrogenation of C or 25C or in the subsequent oxidation of 7d25C or 7dC to ecdysteroid. Rather, the mutation appears to affect the expression of a gene governing the translocation of delta 5,7-sterol intermediates from the subcellular compartment where they are synthesized and/or stored to the site of subsequent oxidation to ecdysteroid.

Metabolism in vitro of cholesterol and 25-hydroxycholesterol by the larval prothoracic glands of Manduca sexta

The prothoracic glands in vitro convert 25-hydroxycholesterol (25C) to 25-hydroxy-7-dehydrocholesterol (7d25C) and to ecdysteroids at a greater rate than cholesterol (C) is converted to ecdysteroids via 7-dehydrocholesterol (7dC). Mediated via a cytochrome P450 most probably located in the endoplasmic reticulum (ER), both intact and extensively homogenized prothoracic glands, as well as crude subcellular fractions, were able to 7,8-dehydrogenate 25C to 7d25C eight-fold more efficiently than they could convert C to 7dC. However, less than a two-fold difference was observed in the subsequent monooxygenase mediated conversion of these two intermediates formed in situ into ecdysteroids, mainly ecdysone (E) and 2-deoxyecdysone (2dE) and/or their 3-dehydroderivatives. When 7dC, and particularly 7d25C, were made directly available to these tissue preparations, their conversion to ecdysteroids greatly exceeded that of the in situ conversion of either C or 25C, via 7dC or 7d25C, respectively. Indeed, there was an eight-fold increase in the VMAX for 25C dehydrogenation by homogenized glands relative to the dehydrogenation of C. Most important, however, was the 1000-fold increase in the VMAX observed for the direct production of E from emulsified 7d25C by gland homogenates relative to E production from 25C via 7d25C synthesized in situ. Thus, it is apparent that even after the rapid and efficient conversion of 25C to 7d25C within the ER, the subsequent rate of conversion of this intermediate to E is greatly retarded relative to that observed following the direct incubation of emulsified 7d25C with gland homogenates. These differential kinetics of direct and indirect 7d25C incorporation into E are interpreted as evidence for the existence of a barrier to the efficient translocation of the delta 5,7-sterol intermediates from the ER to another site where the subsequent, uncharacterized initial conversions leading to ecdysteroids take place. On the basis of studies on mammalian adrenal cortical steroidogenesis, this site is postulated to be the inner membrane/matrix of the mitochondria. The present data support the hypothesis that the translocation of both 7dC and 7d25C, first from the site of their probable synthesis within the ER membranes, next through the cytosol to the outer mitochondrial membrane, and then across the intramitochondrial aqueous space to the inner membrane/matrix compartment, may be analogous to the translocation in the adrenal cortex of ER-derived C, first to the plasma membrane and/or to the outer mitochondrial membrane and then to the inner mitochondrial membrane/matrix for P450scc-mediated conversion into pregnenolone.